CUDA error: out of mem aloc result line 855. Does anyone experience the same issue?
Try rendering using CPU.. because I guess the 8GBs of GPU memory can't handle 13GBs of your scene memory. I've faced with with 4GBs of card and now I only use GPU for testing the scene in realtime live preview and always render with CPU. 

when using GPU, Blender push the whole scene to GPU's memory and then CUDAs start rendering the image. while using CPU, the core starts rendering using CPU's core and threads. 

Edited

Secondly you should try to lower down the memory load on GPU... 8GB is good memory for an average scene. There are many ways to reduce the momory in scene i.e.


if you are using HDRI.. user a step lower in size i.e (if you are using HDRI of 8K, try to use 4k or 2k and see what effects.
If you are using large textures, try to lower down their resolutions too.


You can also try with out all of the textures and see if it renders so quick then start enabling a few and then a few and then a few and each time render the scene with GPU. 

And Last but not lease... try rendering the scene in lower resolution like.. instead of 4k of resolution try rendering in 50% or 25% in scale percentage.

 

If you are still unable to render this.. then as blender says..



https://docs.blender.org/manual/en/latest/render/cycles/gpu_rendering.html